Cephalometric evaluation of soft tissue profile changes following double jaw surgery : (Le Fort I and vertical subsigmoid osteotomy)

Abstract

A retrospective cephalometric study was undertaken to evaluate the soft tissue changes following orthodontic decompensation, Le Fort I osteotomy and surgical setback of the mandible using the technique of intraoral vertical subsigmoid osteotomy. No genioplasty was performed. The investigation involved a detailed analysis of 23 sets of serial cephalometric records consisting of 10 males and 13 females, in the Oral and Maxillofacial Surgery Unit of the University of Adelaide. The female sample ages ranged from 16 years, 2 months to 35 years, 5 months with a mean age of 20 years. The male sample ages ranged from 16 years, 5 months to 59 years, 5 months with a mean age of 20 years. Of the 23 sets of patient records, 23 had cephalograms available within three months prior to surgery and within six months after surgery. 20 subjects (87%) also had cephalograms taken within one year following surgery. 10 subjects (43%) had cephalograms taken within two years after surgery. 9 subjects (21%) had cephalograms taken within three years after surgery. This series was studied for short and long term soft tissue changes. START WITHIN three months PRIOR TO SURGERY WITHIN six months POST SURGERY WITHIN one year POST SURGERY WITHIN two years POST SURGERY WITHIN three years POST SURGERY 23 sets 23 sets 23 sets 20 sets 10 sets 9 sets Standard procedures were used to reduce the effect of random error on the results. These included selection of cases according to radiographic quality, the use of accepted landmark definitions, a standardised method of landmark location, an electronic digitiser to record landmark coordinates and computer plots to identify "wild" recordings. Replicated measurements were made in order to quantify the error component. The error of the method involved in landmark location, superimposition and digitisation was low. For some variables, the differences between the two sets of determinations were found to be significant at the 5% level. In these instances, they were found to require careful interpretation. The error of digitisation alone was not significant. The superimposition method of Björk (1968) and Björk and Skieller (1983) was used in this study. This method, which utilised stable structures of the anterior cranial base, had a sound biological rationale and was of acceptable accuracy. The sample size was small but generally larger than those of previously reported soft tissue studies of a similar nature. Therefore, the results need to be interpreted with some degree of caution. The data was normally distributed allowing the application of routine statistical procedures. Some statistically significant differences were found between the mean value of the male and female groups calculated from the presurgical data. The changes following surgery were generally not statistically significant between males and females. The present study is unique in that it is the first known cephalometric evaluation of soft tissue profile changes following Le Fort I advancement and vertical subsigmoid setback. However, the soft and hard tissue changes appear comparable with other studies using different techniques. Horizontal soft tissue changes of the upper lip were positively correlated to horizontal hard tissue changes of the maxilla: A:SUN 1:0.81 (r=0.80, p<0.05); A:SLS 1:0.74 (r=0.59, p<0.01); A:LS 1:0.53 (r=0.68, p<0.01). soft tissues generally lagged behind the hard tissues. Vertical soft tissue changes of the upper lip were positively correlated to vertical hard tissue changes of the maxilla: A:SUN 1:0.79 (r=0.43, p<0.05); A:SLS 1:0.64 (r=0.18); A:LS 1:0.66(r=0.33). Horizontal and vertical soft tissue changes of the lower lip were positively correlated with horizontal and vertical changes at B-point: Horizontal: B:Ll 1:0.50 (r=0.69,p<0.01); B:lLS 1:0.69 (r=0.93, p<0.01). Vertical: B:lLS 1:0.80 (r=0.56, p<0.01). Changes of the soft tissue chin were positively correlated with changes at pogonion: 1:0.94 (r=0.94, p<0.01). These correlations need to be interpreted cautiously as the sample size is small. The upper lip thinned following maxillary advancement. For every 1 mm of maxillary advancement (at A-point), the upper lip thickness reduces by 0.61 mm (r=0.71, p<0.01). The upper lip lengthened following surgery but this was not statistically significant. The lower lip length reduced following surgery by a minimal amount but this was not statistically significant. This may be due to the lower lip coming under the influence of the upper lip following surgery. Lip competency is established following surgery. During the period six months to twelve months postsurgery, the maxilla moved 43% superiorly and 28"/o backwards. The mandible moved 11% forwards and 34"/" superiorly. Upper incisors proclined during this period. The upper incisor proclination may be due to forward movement of the mandibular arch and postero-superior movement of the maxilla. The lower incisors also proclined during this period but the change was minimal. This may be due to alteration in the position of gonion at surgery since this point was often close to the site of surgery and could have influenced the lower incisor to mandibular plane angle. Ching (1995) reported proclination of lower incisors during this period. The nasolabial angle increased in the presurgery to postsurgery six months period. Labiomental fold deepened in the presurgery to postsurgery six months period. Lip form established at surgery appears to be maintained in the longer term. Thick and thin upper lips responded similarly to surgery. Thick and thin lower lips also responded similarly to surgery. Lip thickness did not seem to influence the surgical response. The magnitude of surgical advancement of the maxilla did not affect the upper lip response. The magnitude of surgical setback did not affect the lower lip response. The soft tissue response is consistent and proportional to the skeletal change. Age and sex do not appear to have a bearing on the soft tissue response of lips following surgery. Minimal skeletal, dental and soft tissue changes were noted 12 months postsurgically indicating stability of the Le Fort I and vertical subsigmoid osteotomy procedure. Most of the correction was maintained at 12 months postsurgery. However, some degree of caution is required when interpreting the data at 24 months and 36 months postsurgery as sample size becomes extremely small.